If the following text appears in the rule “Construction”

An Effect applies only to an Imagineer who has at least one instance of that Building in a Zone they operate. An Effect may specify a constant variance to the gamestate for that Imagineer, or may specify additional actions to be carried out once by that Imagineer when processing a Business Day (multiple instances of a given Building may change the magnitude of an Effect, but do not allow the Imagineer to take such actions more than once per Business Day).

then after it append

If multiple effects take place at the same step of processing a business day, they are applied in alphabetical order by building name.

Otherwise, append the following to the rule “Construction”

An Effect applies only to an Imagineer who has at least one instance of that Building in a Zone they operate. An Effect may specify a constant variance to the gamestate for that Imagineer, or may specify additional actions to be carried out once by that Imagineer when processing a Business Day (multiple instances of a given Building may change the magnitude of an Effect, but do not allow the Imagineer to take such actions more than once per Business Day). If multiple effects take place at the same step of processing a business day, they are applied in alphabetical order by building name.

In either case, add a subrule called “Fountain of Youth” to the rule “Construction” and give it the following text:

Cost: 2000
Size: 1
Effect: After the Local Accounting step but before the File Records step, the processing Imagineer may change the first senior visitor for that Business Day (if one exists) to a child.